Method and apparatus for automatic port interconnection discovery in an optical network

ABSTRACT

To automatically discover the port connections for all nodes in a network, a master node generates a predetermined optical signal and transmits the predetermined optical signal to a neighboring node, which signal identifies the port on which the master node transmitted the predetermined signal. The recipient transmits a reply signal to the predecessor node and to the master node via a control channel, which identifies a port on which the predetermined optical signal was received by the neighboring node. By successively repeating this process in a methodical manner, the master node can discover all of the port interconnections in the optical network. Also each node can discover all its port interconnections to its neighbors. Moreover, by selecting controlling the state (e.g., terminate, open) of the ports of the non-master nodes in the network, the master node can control which nodes receive the predetermined signal, thereby ensuring proper port discovery.

BACKGROUND OF THE INVENTION

[0001] The present invention relates generally to methods andapparatuses for provisioning communications channels intelecommunication or computer networks, and more particularly to amethod and apparatus for provisioning communications channels in atelecommunications or computer network that operates optically.

[0002] Communications networks, including optical communicationsnetworks, generally comprise many nodes at which the data stream iscoupled from one incoming port to an outgoing port to route the datastream to the desired destination. An example of an optical node is anoptical cross-connect or optical add-drop multiplexer.

[0003] In an optical network, in addition to the payload channels, eachnetwork node is sometimes connected to its adjacent or neighboring nodesand a master node by a control channel. Each network node may have manyincoming and outgoing ports, e.g., 4, 8, 16, 64, etc. Each port isconnected to a port on a neighboring node. Multiple ports one on nodemay be connected to the same node on their terminal side. However, eachport on a node is terminated in only one other port.

[0004] When provisioning connections in any network, including opticalnetworks, it is necessary to identify the port interconnections betweenadjacent nodes (e.g., ONNs) before attempting to setup channelconnections, such as optical channel connections in an optical networkcross-connect. Manually identifying the node interconnections andpopulating a port adjacency table in each node is possible, butcumbersome, even if the table is subsequently dynamically updated as andwhen connections are made and released. This is particularly problematicwhen the numbers of ports per node are large. Moreover, as data networksare ever increasing in size, manual techniques for identifying the portswill become increasingly tedious.

[0005] Currently, an automatic method for port interconnection discoveryin all-optical cross-connect-based network does not exist. Although sucha scheme may be feasible in an optical-electrical cross-connect-basednetwork, in which optical-electrical-optical conversion takes place ineach optical network node (ONN), techniques for automated portinterconnection discovery are limited due to the lack of optical toelectrical conversion in an all-optical cross-connect. Moreover, in anoptical communication network, some nodes are not capable of generatingan information-bearing signal that can be transmitted over one of theoptical communications payload channels. This is because the node lacksthe ability to convert a signal from the electrical domain to theoptical domain. It is the precise ability of the node to operatecompletely optically that allows the node to operate at extremely highspeeds. Consequently, requiring an electrical conversion in the processwould unduly limit the operating speed or increase the cost. As aresult, techniques for automatically provisioning nodes in anoptical/electrical communications network are not possible inall-optical communications networks.

[0006] The present invention is therefore directed to the problem ofdeveloping a method and apparatus for automated port interconnectiondiscovery in an optical network employing optical cross-connects thatoperate completely optically (i.e., all-optical).

SUMMARY OF THE INVENTION

[0007] The present invention solves this and other problems by, interalia, generating a predetermined optical signal at a first node,transmitting the predetermined optical signal from the first node to aneighboring node, which signal identifies the port on which the firstnode transmitted the predetermined signal, and transmitting a replysignal from the neighboring node to its predecessor node and to thefirst node via a control channel, which identifies a port on which thepredetermined optical signal was received by the neighboring node. Bysuccessively repeating this process in a methodical manner, the firstnode can discover all of the port interconnections in the opticalnetwork. Also each node can discover all its port interconnections toits neighbors. Moreover, by selecting controlling the state (e.g.,terminate, open) of the ports of the secondary nodes in the network, thefirst node can control which nodes receive the predetermined signal,thereby ensuring proper port discovery.

[0008] In one embodiment of the invention, the first node is a masternode and the secondary nodes are non-master nodes.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 depicts an exemplary embodiment of an optical network towhich various embodiments of a method according to the present inventionare applicable.

[0010]FIG. 2 depicts another exemplary embodiment of an optical networkto which various embodiments of a method according to the presentinvention are applicable.

[0011]FIG. 3 depicts an exemplary embodiment of a method according toone aspect of the present invention.

[0012]FIG. 4 depicts an exemplary embodiment of a packet structure foruse in a variable modulation signal according to another aspect of thepresent invention.

DETAILED DESCRIPTION

[0013] It is worthy to note that any reference herein to “oneembodiment” or “an embodiment” means that a particular feature,structure, or characteristic described in connection with the embodimentis included in at least one embodiment of the invention. The appearancesof the phrase “in one embodiment” in various places in the specificationare not necessarily all referring to the same embodiment.

[0014] The present invention provides, inter alia, a technique for anOptical Network node (ONN) in an optical data network to automaticallydiscover its port interconnections without requiring a signal to begenerated with an optical-cross connect. In this document, ONN and nodeare used interchangeably. As used herein, an optical network node is anynode having one or more incoming ports and one or more outgoing ports.Examples of optical network nodes include: optical cross-connects,optical add-drop multiplexers, optical terminal multiplexers, etc.

[0015] Moreover, herein the terms port and channel are usedinterchangeably. However, a channel is more accurately two ports coupledtogether by a communication medium. Thus, a port is either the input orthe output of a channel, although, herein the terms are often usedinterchangeably.

[0016] Turning to FIG. 1, if one needs to set up an optical channelconnection (e.g., a light path) between node A 101 and node B 102, theonly two possible ports on node A 101 are port 3 and port 6. Of thesetwo ports, port 3 is unavailable (see the ONN A—Port Adjacency Tablebelow). Port Type Port Local Oc48/92/na Available Adjacent Node PortRemote Port 1/2/8 0 = No, 1 = Yes B 3 2 8 0 B 6 11 8 1 C 8 7 8 0 None 4None 1 1

[0017] Hence, port 6 is the only port of choice. Similar to node A 101,node B 102 also maintains its own Port Adjacency Table, hence node Bknows port A6 is connected to port B11.

[0018] The Port Adjacency Table on each node may be manually configuredduring start-up or initialization. At this time, probably all the portswould be marked as “Available”. When a new optical channel connectionneeds to be setup, e.g., between port A4 and port D7 through node B,then the problem is one of determining the right ports on each of node A101, node B 102 and node D 104

[0019] For this example, assume there is already another traffic flowingin channel B6-D3; hence, channel B6-D3 is unavailable. Consequently, theonly possible connection path between node B 102 and node D 104 ischannel B4-D5. As a result, the full connection path between port A4 andport D7 is: path A4-A6-B11-B4-D5-D7.

[0020] Note that in the above case only the source and destinationinformation (A4 and D7) and the intermediate node B 102 are known. Allother intermediate ports (A6 . . . D5) need to be discoveredautomatically.

[0021] To set up a connection between ports A4 and D7 through node B102, ONN A 101 sends a connection request to node D 104 along node B102. For example, the request can be a message such as the following:

[0022] Setup a connection between ports A4 and D7 through node B 102.

[0023] The connection request flows along the control channel 105 only.Control channel 105 is terminated on each node (101-104) and therequest/other information in the control channel 105 is interpreted byeach node (101-104). Hence, the selection of the ports between node B102 and node D 104 will be done by node B 102 and node A 101 is unawareof this selection. After node B 102 selects the ports between node B 102and node D 104, it can signal the information back to node A over thecontrol channel 105.

[0024] Note that all requests for connection (and tear down) flow ONLYover the control channel 105. The other port connections are calledoptical channel connections (also known as data connections or bearerchannels) and these are purely light paths traveling all the way fromthe source CIC card 106 (via port A4) to destination CIC card 107 (viaport D7). It is through the Customer Interface Cards (CICs) present inan optical node that a customer sends and receives his/her data trafficover the network. Using only the control channel 105, one can keep trackof this optical channel connection.

[0025] Based on this connection path, optical cross-connects are made onnode A 101 (A4-A6), node B 102 (B11-B4) and node D 104 (D5-D7), therebyforming an end-to-end optical channel connection. After this, the PortAdjacency Tables in node A 101, node B 102 and node D 104 are updatedand ports A4, A6, B11, B4, D5 and D7 are marked as unavailable (in otherwords, a channel exists from A4-A6-B11-B4-D5-D7). When this connection(A4-A6-B11-B4-D5-D7) is torn down, the above set of ports are remarkedas available for new connections.

[0026] Manual mapping is cumbersome—even for a small network—toaccurately compute and populate the information to all the nodes. Thismanual process may be acceptable for a 16 node, 16-channel (port)network. However, scaling this to a large network with as few as 64channels becomes cumbersome. If mistakes are made in the map table or inthe physical connections during this manual process, diagnosing theerrors is rather difficult.

[0027] High Level View

[0028] According to one aspect of the present invention, the CIC card isenabled to send various special signals (e.g., optical patterns) overthe optical channels, but not the control channel. The special signalsare termed Variable Modulation (VM). VM is encoded in such a way as torepresent a node name and port number (e.g. A6), which information istermed a Label, and which Label is automatically generated. The ONNshave optical monitors on each of its ports, known as Port Monitors (PM).The PM detects the VM and the ONN deciphers the Label. When a nodereceives a Label from its neighbor, (the Label has the neighbor's nodename and the port over which it was sent) it correlates the Label withits own node name and the port on which it was received using the PM.Thus, the node discovers to what neighboring node and port (on thatneighbor) to which that this particular receiving port is connected. Thenode then transfers this Port Adjacency information to that neighbor,and the master node. Thus, two neighboring nodes maintain identical PortInterconnection details.

[0029] The mechanisms of generating the right Label, directing it to theright destination, coordinating orderly discovery of the PortInterconnections between neighbors over an entire network are describedin subsequent paragraphs.

[0030] Variable Modulation

[0031] Variable Modulation is a low frequency signal, compared to thehigh bit-rate of the optical channels, which low frequency signal can begenerated by a CIC card. As the name modulation indicates, VM is a userdefinable signal or pattern. A CIC card can generate VM only when it isnot generating its normal payload traffic, i.e., when it is idle. Inother words, the system does not mix VM with real traffic.

[0032]FIG. 4 depicts the packet format of the VM signal. One possibleembodiment of the VM signal is a 4×32-bit packet. The first 2×32 bitsconsist of framing to enable the recipient to determine the start of avalid VM packet. The next 32 bits comprise the label, e.g., node ID andport ID. A 16-bit cyclic redundancy code is appended to the end toenable error detection. In this embodiment, a remaining 16 bits isunused.

[0033] Port (ONN) Modes

[0034] The ports on the ONN can be put in OPEN and TERMINATE modes. Inthe OPEN mode, the ports allow light to pass through them to anotherport—this can be its connected port on its neighbor or can be anotherport on the same node to which it is cross-connected. In the TERMINATEmode, as the name indicates, no light is allowed to pass through.

[0035] Port Interconnection Discovery Mechanism

[0036] Turning to FIG. 2, one (or more) ONN that has at least one CICcard is configured as the Master. The information as to which node isthe Master is configured in all the ONNs. All the ports in the Masterare in the OPEN mode. All other ONN ports are in TERMINATE mode.

[0037] Master A has an CIC card attached to port 1 and uses this CICcard to launch VM signals to the network. Master A launches VM signalsthrough each of its other ports successively (2, 3 and 4).

[0038] First Master A launches the VM signal through port 2 (i.e.,Master A does a cross-connect in A, A1-A2). The Label (i.e., VM) is A2(this encoding is automatically done by software). The signal A2 isreceived by the neighboring ONN B on port 1, which is detected by theport monitor on B. Hence, node B knows that B1 is connected to A2. NodeB then informs this A2-B1 interconnection information to node A, throughthe control channel, not shown. Next, node B puts both its ports 1 and 3in the OPEN mode and cross-connects 1 and 3. Next, a new signal islaunched by A1 and it goes to C1 through A1-A2-B1-B3. The Label in thiscase is encoded as B3. Node C on receiving this on port 1 knows thatB3-C1 is interconnected and informs this to B.

[0039] Master node A then sends a signal from A1 to A3 and thereon to B2for identifying the A3-B2 interconnection. In this case, the Label sentis A3. Then Node A probes A4-D1 and so on. The Label information issoftware configurable and it is always a destination node's predecessornode ID and port number.

[0040] Reliable Discovery Algorithm

[0041] In a large network, it is essential to send the VM signals in anorderly manner over one node after another and one port and another forcomplete discovery of all the port interconnections. All the nodesperiodically inform the Master as to which of their ports are still tobe discovered, thereby prompting the Master to send VM signals in theirdirection.

[0042] Turning to FIG. 3, shown therein is a method for automaticallydiscovering the port interconnections in a network whose nodes and portconnections are totally unknown. As part of the network initialization,each node is designated either a master node or a non-master (sometimesknown as slave) mode. Each network, or network neighborhood, has adesignated master node. The remaining nodes are non-master or slavenodes. Each node knows which node in the network or network neighborhoodis the master node and what type of node it is designated. Typically,the master nodes have the CIC cards with the ability to generate theabove-described variable modulation signal. Moreover, each node has acommunication channel to the master node (or its neighboring node) viathe control channel.

[0043] When a network is first initialized, the nodes do not know theports of other nodes to which their ports are connected. Upon startup,each node sends a connection request to the master node indicating theports in it and requesting information as to which other nodes' portsits ports are connected. Upon receipt of all of these requests, themaster node creates a port adjacency table for the network. This tableidentifies all of the ports in the network for each node, and includes afield for the node/port to which each port is connected. As informationis collected regarding these connections, the master node updates thistable.

[0044] Referring to FIG. 3, the process begins in step 31. First, allports in all non-master nodes are placed in the TERMINATE state (step32). This ensures that signals will only reach the nodes neighboring themaster node (also referred to as the first level nodes).

[0045] The master node discovers all of its port connections bysuccessively transmitting the variable modulation signal to all of itsports (step 33). The master node transmits successively over each of itsnodes a predetermined signal, e.g., the variable modulation signaldiscussed above. The predetermined signal has encoded thereon the nodeand port from which the signal originates. The signal is thentransmitted from this port to the connection at the other end of theport.

[0046] Upon receipt of this predetermined signal, the recipient nodedecodes the encoded information and replies with the port on which thepredetermined signal was received to the master node via the controlchannel (step 34).

[0047] Now the master node knows which port on the recipient node isconnected to the port on which it transmitted the predetermined signal.The master node then updates the port adjacency table (step 35). Eachrecipient node also updates its port adjacency table (step 36).

[0048] The above process continues until all of the ports in the masternode's port adjacency table are identified. This is tested throughoutthe process (step 37). Those ports in those nodes whose port connectionsare completely known are then placed in the OPEN state, which allowsthem to pass through VM signals (step 38). The master then successivelysends VM signals to the next level nodes whose port connections remainunknown (step 38). The VM signals in these cases are labels with thenode/port identification of the ports in the next level whoseconnections remain unknown. The process returns to step 34 and repeats,whereby the port connections of the next level from the master nodeshould be completely discovered. Again, it is tested whether thereremain any ports whose connections are not known. The above processcontinues to the next level until all port connections are known.

[0049] Alternatively, the master node could select a port from the portadjacency table that remains unidentified as to its connection. Themaster node then addresses the predetermined signal to that port. Forexample, if node B has a port 3, the connection to which remainsundiscovered, the master node transmits the predetermined signal to nodeB to be transmitted from node B port 3. The recipient of thepredetermined signal then informs its predecessor node and the masternode via the control channel as to the port on which the predeterminedsignal encoded with “B3” was received. The predecessor node and themaster nodes then update the port adjacency table with this information.This process continues until all undiscovered ports are discovered.

[0050] After the initial configuration of a network if a new node comeson-line, then this new node is configured as a Secondary Master. Unlikethe Master, the role of a Secondary Master is limited to discoveringport inter-connections to its neighbors only. A Secondary Master cannotdiscover remote nodes port interconnections. The discovery process ofthe Secondary Master itself is identical to the Master except that itstops after discovering its immediately connected neighbor ports. Itshould be noted that there might be several Secondary Master nodes in anetwork, as each newly joined node is configured as a Secondary Master.

[0051] If any ports in any nodes remain undiscovered, the node whoseport connections remain unknown sends a connection request to the masternode and the port connection is thus discovered, as described above.

[0052] Although various embodiments are specifically illustrated anddescribed herein, it will be appreciated that modifications andvariations of the invention are covered by the above teachings andwithin the purview of the appended claims without departing from thespirit and intended scope of the invention. For example, while severalof the embodiments depict the use of specific data formats andprotocols, any formats and protocols will suffice. Moreover, while someof the embodiments describe specific embodiments of ONNs, others apply.Furthermore, these examples should not be interpreted to limit themodifications and variations of the invention covered by the claims butare merely illustrative of possible variations.

What is claimed is:
 1. A method for automatically discovering portinterconnections in an optical network comprising: transmitting apredetermined optical signal from a first available port of a first nodein the optical network to a second node in the optical network, saidpredetermined optical signal including node origination information andport origination information; receiving the predetermined optical signalat the second node in the optical network; determining on which port thepredetermined optical signal was received by the second node in theoptical network; and forwarding a reply signal to the predecessor nodeand to the first node from the second node over a control channel of theoptical network, said reply signal including node terminationinformation and port termination information.
 2. The method according toclaim 2 wherein said first node is a master node and said second node isa non-master node.
 3. The method according to claim 2, furthercomprising updating a port adjacency table in the master node uponreceipt of the reply signal.
 4. The method according to claim 2, furthercomprising transmitting a second predetermined optical signal over asecond available port, wherein the second predetermined optical signalincludes node origination information and port origination information.5. The method according to claim 2, further comprising receiving aconnection discovery request signal from a non-master node in theoptical network at the master node in the optical network andtransmitting the first predetermined optical signal in response to saiddiscovery request signal.
 6. The method according to claim 2, furthercomprising designating a new node that comes online in the opticalnetwork as a secondary master node, and limiting a port interconnectiondiscovery capability of the secondary master node to only immediateneighbors of the secondary master node.
 7. The method according to claim6, further comprising transmitting a second predetermined optical signalfrom a first available port of a secondary master node in the opticalnetwork to a non-master node in the optical network, said predeterminedoptical signal including node origination information and portorigination information.
 8. The method according to claim 7, furthercomprising: receiving the second predetermined optical signal at thenon-master node in the optical network; and determining on which portthe predetermined optical signal was received by the non-master node inthe optical network.
 9. The method according to claim 8, furthercomprising forwarding a reply signal to the secondary master node fromthe non-master node over a control channel of the optical network, saidreply signal including node termination information and port terminationinformation.
 10. A method for automatically discovering connections inan optical network comprising: transmitting a predetermined signal froma first available port of a first node in the optical network to asecond node in the optical network, said predetermined signal includingnode origination information and port origination information; receivingthe predetermined signal at the second node in the optical network;determining on which port the predetermined signal was received by thesecond node in the optical network; and forwarding a reply signal to thepredecessor node and to the first node from the second node over acontrol channel of the optical network, said reply signal including nodetermination information and port termination information.
 11. The methodaccording to claim 10 wherein said first node is a master node and saidsecond node is a non-master node.
 12. The method according to claim 11,further comprising updating a port adjacency table in the master nodeupon receipt of the reply signal.
 13. The method according to claim 10,further comprising transmitting a second predetermined optical signalover a second available port, wherein the second predetermined opticalsignal includes node origination information and port originationinformation.
 14. The method according to claim 10, further comprisingreceiving a connection discovery request signal from a non-master nodein the optical network at the master node in the optical network andtransmitting the first predetermined optical signal in response to saiddiscovery request signal.
 15. The method according to claim 10, furthercomprising designating a new node that comes online in the opticalnetwork as a secondary master node, and limiting a port interconnectiondiscovery capability of the secondary master node to only immediateneighbors of the secondary master node.
 16. The method according toclaim 15, further comprising transmitting a second predetermined signalfrom a first available port of a secondary master node in the opticalnetwork to a non-master node in the optical network, said predeterminedsignal including node origination information and port originationinformation.
 17. The method according to claim 16, further comprising:receiving the second predetermined signal at the non-master node in theoptical network; and determining on which port the predetermined signalwas received by the non-master node in the optical network.
 18. Themethod according to claim 17, further comprising forwarding a replysignal to the secondary master node from the non-master node over acontrol channel of the optical network, said reply signal including nodetermination information and port termination information.
 19. A methodfor automatically discovering a plurality of port connections in anall-optical communications network comprising: a) transmittingsuccessively a predetermined signal, having a label identifying at leastan originating node and outgoing port, over each of a plurality ofoutgoing ports of a master node; b) replying from each recipient of thepredetermined signal via a control channel indicating on which incomingport for each recipient the predetermined signal with a given label wasreceived; c) updating a port adjacency table in at least the master nodeupon receipt of the reply signal; d) placing all nodes whose portconnections are known in an open state; e) transmitting successively apredetermined signal, having a label identifying at least an originatingnode and outgoing port, over one or more of a plurality of outgoingports of a next level node having unknown port connections; and f)repeating steps b) through e) until all port connections in all nodesare discovered.
 20. The method according to claim 19, wherein saidreplying occurs from said each recipient to at least the master node.21. The method according to claim 20, wherein said replying occurs fromsaid each recipient to at least the master node and a predecessor nodeof said recipient.
 22. The method according to claim 19, furthercomprising placing all non-master nodes in a terminate state before stepa) of transmitting.
 23. The method according to claim 19, furthercomprising updating a port adjacency table in the recipient'spredecessor node.
 24. The method according to claim 19, furthercomprising designating a new node that comes online in the all-opticalcommunications network as a secondary master node, and limiting a portinterconnection discovery capability of the secondary master node toonly immediate neighbors of the secondary master node.
 25. A method forautomatically discovering a plurality of port connections in anall-optical communications network comprising: a) transmittingsuccessively a predetermined signal, having a label identifying at leastan originating node and outgoing port, over each of a plurality ofoutgoing ports of a first node; b) receiving from each recipient of thepredetermined signal a reply signal indicating on which incoming portfor each recipient the predetermined signal with a given label wasreceived; c) updating a port adjacency table in at least the first node;d) placing all nodes whose port connections are completely known in anopen state; e) transmitting successively a predetermined signal with alabel identifying at least an originating node and outgoing port overone or more of a plurality of outgoing ports of a next level node havingunknown port connections; and f) repeating steps b) through e) until allport connections in all nodes are discovered.
 26. The method accordingto claim 25, wherein said reply signal is received from said eachrecipient by at least the first node.
 27. The method according to claim25, wherein said reply signal is received from said each recipient by atleast the first node and a predecessor node of said recipient.
 28. Themethod according to claim 25, further comprising placing all secondarynodes in a terminate state before step a) of transmitting.
 29. Themethod according to claim 25, further comprising updating a portadjacency table in the recipient's predecessor node.
 30. The method ofclaim 25 wherein said first node is a master node.
 31. The methodaccording to claim 30, further comprising designating a new node thatcomes online in the all-optical communications network as a secondarymaster node, and limiting a port interconnection discovery capability ofthe secondary master node to only immediate neighbors of the secondarymaster node.
 32. A method for automatically discovering one or more portinterconnections in an optical network comprising: receiving aconnection request signal from a requesting node indicating that aterminus of one or more of its outgoing ports' remains undiscovered;transmitting a predetermined optical signal from a first node to therequesting node, said predetermined optical signal including a labelidentifying the requesting node and one outgoing port of the requestingnode; outputting the predetermined optical signal from the requestingnode via said one port identified in the label; and receiving a replysignal from a recipient of the predetermined optical signal via acontrol channel, said reply indicating a recipient port and a recipientnode of the predetermined optical signal.
 33. The method according toclaim 32, further comprising updating a port adjacency table uponreceipt of said reply signal.
 34. The method according to claim 32,further comprising updating a port adjacency table in the first node andthe requesting node upon receipt of the reply signal by the master nodeand the requesting node.
 35. The method according to claim 32, furthercomprising transmitting a reply signal upon receipt of the predeterminedsignal to the first node and a predecessor node via a control channel.36. The method of claim 32 wherein said first node is a master node. 37.The method of claim 34 wherein said first node is a master node.
 38. Themethod according to claim 36, further comprising designating a new nodethat comes online in the optical network as a secondary master node, andlimiting a port interconnection discovery capability of the secondarymaster node to only immediate neighbors of the secondary master node.